The invention relates to a multielement analytical method of the type in which a sample of the substance to be analyzed is burned with a reactant and then analyzed.
The most important and quantitative micro- and ultramicromethods for organic materials involving decomposition and separation are based on the combustion of compounds in oxygen at 1,000.degree. to 2,000.degree.. The products of combustion consist of highly volatile oxides (H.sub.2 O, CO.sub.2 and SO.sub.2) and elements (N.sub.2, Cl.sub.2, Br.sub.2 and I.sub.2) and sparingly volatile or non-volatile oxides (ash). The assay of the readily volatile materials is undertaken sequentially with element-specific methods. H.sub.2 O, CO.sub.2 and N.sub.2 (in CHN analysis) are for instance determined simultaneously by gas chromatography, a process which may be also modified for the determination of SO.sub.2 as well (S analysis, see E. Pella, B. Colombo, Mikrochim. Acta (Vienna), 1973, pages 697 to 719).
Despite comminution and the use of high temperatures, the combustion of inorganic materials in oxygen is frequently incomplete, since the oxygen compounds formed are mostly non-volatile. Instrumental methods are limited to the determination of the elements hydrogen, carbon and sulfur using two different devices. For determining different concentration ranges several instruments are required. The German patent 3,036,959 describes an extraction method for the volatilisation of the elements to be determined by reaction with non-volatile fluorides and chlorides in a metallic melt under conditions which are experimentally difficult to maintain followed by gas analysis of the volatile halides. Part of the volatile halides described--which are analysed in the gaseous phase--do not exist under the conditions described, and certainly include the hexafluorides IrF.sub.6, MoF.sub.6, OsF.sub.6 ReF.sub.6 and UF.sub.6, which are reduced to non-volatile, lower fluorides by metals.
Organic materials are fluorinated at 80.degree. C. and the products of such fluorination analyzed by gas chromatography. Owing to their aggressive action of the fluorine and the hydrogen fluoride on the filling material of the separating column, fluorine and hydrogen are removed prior to gas chromatography by absorption. In this method it is possible to use the inert fluorides CF.sub.4 and SF.sub.6 and the elements oxygen and nitrogen for the determination of carbon, sulfur, oxygen and nitrogen (see K. Asai and D. Ishii, J. Chromatogr. 69 (1972), pages 355/8). The said elements may be determined very much more simply and accurately by oxygen combustion analysis as initially mentioned.